Pacemakers of that kind for biventricular stimulation are basically known and are employed in particular for cardiac resynchronization therapy (CRT).
Cardiac pacemakers generally serve to stimulate in particular a human heart to perform contractions by means of electrical stimulation pulses when such contractions do not occur or do not occur at the correct time, in a natural manner.
It is known to establish moments in time or time windows at which such a cardiac pacemaker expects a natural contraction. If a natural contraction of that kind occurs, an artificial stimulation pulse is generally suppressed (inhibited), which otherwise is delivered at the most appropriate moment in time. It is also known, under given circumstances and depending on the mode of operation of the cardiac pacemaker, to deliver a stimulation pulse at any event, irrespective of whether a natural contraction is or is not detected. The pacemaker operating modes related thereto are uniformly internationally identified by the third letter of a three-letter code such as “VVI” or “DDD”.
Suitable moments in time can be ascertained in various different ways. For example, the physiologically suitable times for a contraction of the right ventricle of a heart can be ascertained by sensing the right atrium of a heart. The natural or the stimulated contraction of the right ventricle takes place after an atrio-ventricular delay time which is such as to afford a pump effectiveness which is as optimum as possible due to the contraction of the atrium and the ventricle which occur in succession in respect of time.
In addition it is also known if necessary to stimulate the atrium.
The heart rate which is predetermined by the pacemaker can in all cases be derived artificially from a measurement value which is characteristic in respect of the physiological demand of a patient if it is not predetermined in the case of atrium-synchronous stimulation by a natural and healthy atrial rhythm. In that respect the physiological demand depends on a condition of exertion or excitation on the part of the patient. In the case of a rate-adaptive pacemaker of that kind, physiologically adequate determination of a stimulation rate can also be effected by determining the intracardiac impedance for a respective cardiac cycle and deriving a suitable stimulation rate from that impedance value.
The indicated operating modes generally concern pacemakers which are either adapted to record excitation potential in the right ventricle and deliver stimulation pulses to a right ventricle or additionally also to record excitation potential in the right atrium and possibly deliver stimulation pulses to the right atrium. The pacemaker operating modes related thereto are internationally uniformly identified by the three-letter code such as for example DDD or VVI.
In recent times, besides the right atrium and the right ventricle, the left ventricle is also stimulated. That is frequently effected simultaneously with the right ventricle, but can also take place with a certain delay relative to the left ventricle. A cardiac pacemaker therapy for the heart, which is linked thereto, is referred to as cardiac resynchronization therapy (CRT).
A biventricular pacemaker in which the interventricular delay time is adjustable and which evaluates a measured bioimpedance of the patient is known from US Patent Publication No 2001/0012953.
The invention relates in particular to the aspect of optimum biventricular stimulation, which can supplement all the above-indicated aspects of a pacemaker. The object of the invention is in particular to provide a pacemaker for optimized cardiac resynchronization therapy.